When providing a supporting structure for a ground based radar it is highly desirable and often necessary to elevate the radar well above ground level to raise it clear of ground clutter obstructions of a local nature such as buildings, trees, hills, vehicles, fences, etc. This is particularly true of a mobile radar unit because there is the expectation that the unit will be moved from one operational location to another as dictated by the exigencies of the situation. The use of a mast which can raise the radar antenna provides savings in the time required to set up the radar and render it operational, since such elevation reduces or eliminates the need to clear the land of local obstructions.
In uses wherein the radar is required to achieve a high degree of angular precision and wherein its antenna is elevated on a tower structure, it has been necessary using prior art techniques to provide a massive tower structure to obtain platform rigidity. In an effort to reduce the weight of such towers, guy wires have often been substituted for massive construction, but experience has shown that guyed structures can only be used where low angular precision is required because of the difficulty in providing high tension in the wires while maintaining the plural wire tensions uniform.
Moreover, conventional support towers are subject to distorting forces which introduce angular errors, such forces including windage, thermal expansion and contraction of non-symmetrical cross-sections, and unequal heating in various parts of the tower structure due to non-uniform exposure to sunlight. Unequal temperature effects produce rotational movements at the top of the tower with respect to the ground, generally about all three axes, i.e. rotation about azimuth, and tilt about level and cross-level. These rotational movements produce errors in the radar determinations of the positions of targets being tracked. The magnitude of errors in level and cross-level due to solar and wind effects on ordinary open-truss structural steel towers set in concrete foundations range in the vicinity of 1.0 to 3.0 milliradians for towers whose height is comparable to the presently disclosed tower, i.e. about 25 feet. When compared with the magnitude of errors in level and cross-level introduced by a precision radar itself, which range in the vicinity of 0.1 to 0.25 milliradian, it will be seen that the errors introduced by an open-truss tower are about ten times greater. Moreover, the towers described above are not suitable for mobile purposes.
Furthermore, when a fixed tower is used, its size and weight and windage responses are further increased by the necessity of providing access to the antenna for repair and maintenance, since such a tower must be fitted with stairs or ladders, and with work platforms and railings located at the top of the tower.
When prior art towers are used in support of military operations their greater size and weight is particularly detrimental because it decreases their mobility and therefore increases their vulnerability. Often a high degree of mobility with short set-up and tear-down times is the best means of protection against enemy observation and enemy fire. This is especially true during intervals between missions while the radar is not in actual use, whereupon the radar antenna can be retracted so that it is no longer exposed above the terrain where it is in full view and even serves to locate other vulnerable equipment as well as personnel. The conventional tower suffers from the further disadvantage of exposing radar repairmen to enemy fire when they must climb the tower to service or repair the antenna.